---
title: "Observing the World: The Five Senses"
book: "Primary & Middle School Physics"
subject: physics
language: en
chapter: 1
exercises: 9
source: https://one-course.com/books/physics/1/en/chapter/1-observing-the-world-the-five-senses
---

# Chapter 1 — Observing the World: The Five Senses

A bird sings somewhere above you. The bread smells warm. The pavement feels cold through your socks. Before doing anything else, physics looks, listens and touches: this chapter is about observing the world with the five senses — and about the tricks they can play on us.

## 1.1 The five senses

**Definition 1.1 (The five senses).**

A *sense* is a way the body finds out about the world. We have five:

1. *sight* — the eyes see light, colors and shapes;
2. *hearing* — the ears hear sounds;
3. *touch* — the skin feels rough or smooth, warm or cold;
4. *smell* — the nose smells the warm bread;
5. *taste* — the tongue tastes sweet, salty, sour.

![The five senses: eye, ear, hand, nose, tongue — five doors between the world and you.](https://one-course.com/images/onecourse/chapters/physics-1/g1-five-senses/fig-0fe3fc76d3c6.svg)

*The five senses: eye, ear, hand, nose, tongue — five doors between the world and you.*

**Example 1.2 (One apple, five senses).**

Eating an apple uses every sense: you *see* its red skin, you *feel* it smooth and round in your hand, you *hear* the crunch, you *smell* its perfume, you *taste* its sweet juice. Five senses, one apple.

![One apple for all five senses: the eyes see its red, the hand feels its smooth skin, the ears heard the crunch of the missing bite, the nose smells its perfume, the tongue keeps the taste.](https://one-course.com/images/onecourse/chapters/physics-1/g1-five-senses/img-a69063206f67.jpg)

*One apple for all five senses: the eyes see its red, the hand feels its smooth skin, the ears heard the crunch of the missing bite, the nose smells its perfume, the tongue keeps the taste.*

**Example 1.3 (Try it: the sound walk).**

Sit still, close your eyes, and count the sounds around you for a little while: a car, a voice, the wind, your own breathing. With eyes closed, the ears notice sounds that the busy eyes made you miss. Most people find $4$ or $5$ sounds they had not noticed before.

**Remark 1.4 (Senses that protect us).**

The senses are also guards. The nose smells smoke before the eyes see a fire; the skin pulls the hand back from a hot pan; a bitter taste warns “do not swallow this”. Never taste or smell something unknown on purpose: ask an adult first. The guards work best when we treat them carefully.

## 1.2 Observing carefully

Looking is not yet observing. Everyone has *seen* a ladybug; who can say how many legs it has?

**Definition 1.5 (Observation).**

To *observe* is to use the senses carefully, on purpose, to answer a question — and then to say or draw exactly what was noticed, not what was expected. An *observation* is what careful watching found out.

**Method 1.6 (How to observe).**

1. Choose a question: *how many legs does the ladybug have?*
2. Watch (or listen, or touch) slowly, without hurrying;
3. say what you notice with precise words: not “it is small”, but “it is smaller than my fingernail”;
4. draw or tell it, so someone else can check.

A good [observation](#def-g1-five-senses-observation) can be checked by a friend: if you both look, you should both find $6$ legs.

**Example 1.7 (Precise words).**

Compare “the stone is nice” with “the stone is gray, smooth, round, and colder than my hand”. The second sentence is an [observation](#def-g1-five-senses-observation): another child can pick that stone out of a whole basket.

![Observing a ladybug: careful eyes count 4 spots on this one — and always 6 legs.](https://one-course.com/images/onecourse/chapters/physics-1/g1-five-senses/fig-45a7b2d3e3cf.svg)

*Observing a ladybug: careful eyes count $4$ spots on this one — and always $6$ legs.*

## 1.3 When the senses are fooled

The senses are wonderful, but they can be tricked. That is exactly why, in the chapters to come, we will learn to *measure*.

**Example 1.8 (Two lines).**

In the picture below, which line is longer? Almost everyone answers “the top one”. Now check with a piece of string: the two lines are exactly as long as each other. The eyes were fooled by the arrow tips.

![The famous trick of the arrow tips: both lines are the same length. Check with a string!](https://one-course.com/images/onecourse/chapters/physics-1/g1-five-senses/fig-8cd915b739ef.svg)

*The famous trick of the arrow tips: both lines are the same length. Check with a string!*

**Example 1.9 (Try it: three bowls).**

Ask an adult to prepare three bowls of water: one cool, one lukewarm, one comfortably warm. Keep one hand in the cool bowl and the other in the warm bowl while you slowly count to $20$. Then put both hands together in the middle bowl: the same water feels warm to one hand and cool to the other! Touch alone cannot be trusted about hot and cold — the next chapter takes up exactly this problem.

**Remark 1.10 (Helpers for the senses).**

People build tools that help the senses: glasses and magnifying glasses help the eyes, a doctor’s stethoscope helps the ears. Later in this book, tools called *instruments* will do even better: they will turn looking and touching into counting and measuring, and counting is much harder to fool.

## 1.4 Exercises

**Exercise 1.1 ★.**

Name the five senses, and for each one the part of the body that does the job.

**Solution of Exercise 1.1.**

Sight — the eyes; [hearing](#def-g1-five-senses-senses) — the ears; touch — the skin; smell — the nose; taste — the tongue.

**Exercise 1.2 ★.**

Which sense tells you: (a) that the radio is on? (b) that the soup is too salty? (c) that your pullover is scratchy? (d) that the lights went out?

**Solution of Exercise 1.2.**

(a) [Hearing](#def-g1-five-senses-senses). (b) Taste. (c) Touch. (d) Sight.

**Exercise 1.3 ★.**

A cake is baking in the oven, door closed, in another room. Which sense finds it first? Which senses will you use when you finally get a slice?

**Solution of Exercise 1.3.**

Smell finds the cake first — the perfume slips under the door. Eating the slice uses sight, touch, smell and taste, and even [hearing](#def-g1-five-senses-senses) if the crust crunches.

**Exercise 1.4 ★.**

Do the sound walk of [Example 1.3](#ex-g1-five-senses-sounds): eyes closed, count the sounds around you. How many did you hear? Which one surprised you?

**Solution of Exercise 1.4.**

Answers vary; most children count $4$ or $5$ sounds, and the surprise is often a quiet one — the refrigerator humming, or their own breathing.

**Exercise 1.5 ★.**

Give an [observation](#def-g1-five-senses-observation) of your shoe using three precise words, as in [Example 1.7](#ex-g1-five-senses-words). “Nice” and “pretty” are not allowed!

**Solution of Exercise 1.5.**

For example: “My shoe is blue, rubbery, and longer than my hand.” Any three precise words that a friend could check are correct.

**Exercise 1.6 ★.**

Ana says: “The cat is soft.” Bob says: “The cat is the best cat.” Which sentence is an [observation](#def-g1-five-senses-observation), and which sense made it? What is the other sentence?

**Solution of Exercise 1.6.**

Ana’s sentence is the [observation](#def-g1-five-senses-observation), made by touch. Bob’s sentence is an opinion: nobody can check “best” by looking or touching.

**Exercise 1.7 ★.**

Which sense warns you of each danger: (a) smoke somewhere in the house; (b) a pan too hot to hold; (c) a car coming from behind you?

**Solution of Exercise 1.7.**

(a) Smell. (b) Touch — the skin feels the heat, even from a small distance. (c) [Hearing](#def-g1-five-senses-senses).

**Exercise 1.8 ★.**

A friend closes their eyes. You put a spoon, a sponge and a pebble in front of them, one at a time. Can they name all three just by touch? Which was easiest to recognize?

**Solution of Exercise 1.8.**

Touch alone names all three easily: metal spoon (hard, cold, smooth), sponge (soft, light), pebble (hard, heavy, round). The spoon is usually easiest — cold metal is hard to mistake.

**Exercise 1.9 ★★.**

Look at the two lines of [Example 1.8](#ex-g1-five-senses-lines). Explain to a friend how to find out for sure which line is longer, without trusting the eyes. Can your method also compare a line with a curvy piece of string?

**Solution of Exercise 1.9.**

Lay a piece of string along the first line and cut or pinch it to the same length, then lay it along the second line: the string compares them without the eyes deciding. The same string can follow a curvy line too, then be pulled straight — so the method even compares a curve with a straight line.